U.S. patent application number 13/428682 was filed with the patent office on 2012-07-19 for mask health monitor using a faraday probe.
This patent application is currently assigned to VARIAN SEMICONDUCTOR EQUIPMENT ASSOCIATES, INC.. Invention is credited to Nicholas P.T. Bateman, Russell J. Low, Benjamin B. RIORDON, William T. Weaver.
Application Number | 20120181443 13/428682 |
Document ID | / |
Family ID | 43037126 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120181443 |
Kind Code |
A1 |
RIORDON; Benjamin B. ; et
al. |
July 19, 2012 |
MASK HEALTH MONITOR USING A FARADAY PROBE
Abstract
In an ion implanter, an ion current measurement device is
disposed behind a mask co-planarly with respect to a surface of a
target substrate as if said target substrate was positioned on a
platen. The ion current measurement device is translated across the
ion beam. The current of the ion beam directed through a plurality
of apertures of the mask is measured using the ion current
measurement device. In this manner, the position of the mask with
respect to the ion beam as well as the condition of the mask may be
determined based on the ion current profile measured by the ion
current measurement device.
Inventors: |
RIORDON; Benjamin B.;
(Newburyport, MA) ; Bateman; Nicholas P.T.;
(Reading, MA) ; Weaver; William T.; (Austin,
TX) ; Low; Russell J.; (Rowley, MA) |
Assignee: |
VARIAN SEMICONDUCTOR EQUIPMENT
ASSOCIATES, INC.,
Gloucester
MA
|
Family ID: |
43037126 |
Appl. No.: |
13/428682 |
Filed: |
March 23, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12845665 |
Jul 28, 2010 |
8164068 |
|
|
13428682 |
|
|
|
|
61229852 |
Jul 30, 2009 |
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Current U.S.
Class: |
250/395 |
Current CPC
Class: |
H01L 31/0682 20130101;
H01J 2237/31711 20130101; H01J 2237/24528 20130101; H01J 2237/24507
20130101; H01L 21/266 20130101; H01L 21/2658 20130101; Y02E 10/547
20130101; Y02P 70/50 20151101; Y02P 70/521 20151101; H01L 31/1804
20130101; H01J 37/3171 20130101; H01L 21/26513 20130101; H01L
31/0288 20130101 |
Class at
Publication: |
250/395 |
International
Class: |
G01T 1/17 20060101
G01T001/17 |
Claims
1. A method for determining the condition of a mask used in an ion
implanter comprising: directing an ion beam through a plurality of
apertures of a mask toward a platen configured to support a target
substrate; translating an ion current measurement device between
said mask and said platen parallel to a location of said target
substrate during implantation; detecting an ion beam current
incident on said ion current measurement device during said
translating, wherein said ion beam current is associated with each
of said apertures; generating a current signal in response to said
ion beam current at a plurality of positions behind said mask;
creating a current profile for each of said apertures based on said
current signal at said plurality of positions; and determining a
dimension of each of said apertures based on said current
profile.
2. The method of claim 1 further comprising determining if one of
said apertures has exceeded a threshold for said dimension.
3. The method of claim 1 further comprising determining if one of
said apertures is less than a threshold for said dimension.
4. The method of claim 1 further comprising determining if said
mask has fractured based on said determining said dimension.
5. The method of claim 1, wherein said dimension is a width of said
aperture.
6. The method of claim 1, wherein said ion current measurement
device is parallel to a length of said apertures.
7. The method of claim 1, further comprising determining a
temperature of said mask based on said dimension.
8. The method of claim 1, wherein said ion current measurement
device is at an angle with respect to said apertures.
9. A method for determining the condition of a mask used in an ion
implanter comprising: directing an ion beam through a plurality of
apertures of a mask toward a platen configured to support a target
substrate, said mask being positioned orthogonally with respect to
said ion beam, each of said apertures having a dimension; disposing
an ion current measurement device behind said mask co-planarly with
respect to said target substrate as if said target substrate was
positioned on said platen and orthogonal with respect to said ion
beam; translating said ion current measurement device across said
ion beam; detecting an ion beam current incident on said ion
current measurement device through said apertures at a plurality of
positions as said ion current measurement device translates across
said ion beam such that said ion beam current is associated with
said dimension of each of said apertures; generating a current
signal in response to said ion beam current from said ion current
measurement device at each of said positions; creating a current
profile for each of said apertures based on said current signal as
said ion current measurement device translates across said ion
beam; and determining said dimension of each of said apertures.
10. The method of claim 9 further comprising changing an angle of
said ion current measurement device with respect to said apertures
of said mask.
11. The method of claim 9 further comprising determining if one of
said apertures has exceeded a threshold for said dimension.
12. The method of claim 9 further comprising determining if one of
said apertures is less than a threshold for said dimension.
13. The method of claim 9, wherein said dimension is a width of
said aperture.
14. The method of claim 9, wherein said ion current measurement
device is parallel to a length of said apertures.
15. The method of claim 9, further comprising determining a
temperature of said mask based on said dimension.
16. The method of claim 9, wherein said ion current measurement
device is at an angle with respect to said apertures.
Description
RELATED APPLICATIONS
[0001] This patent application is a continuation application of
U.S. patent application Ser. No. 12/845,665, filed Jul. 28, 2010,
which claims priority to U.S. Provisional Patent Application Ser.
No. 61/229,852, filed Jul. 30, 2009, both of which are hereby
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention relate to the field of device
fabrication. More particularly, the present disclosure relates to
ion implantation through a mask and a device and system to monitor
the health of the mask used during ion implantation.
[0004] 2. Discussion of Related Art
[0005] Ion implantation is a standard technique for introducing
conductivity-altering impurities into substrates. A precise doping
profile in a substrate and associated thin film structure is
critical for proper device performance. Generally, a desired
impurity material is ionized in an ion source, the ions are
accelerated to form an ion beam of prescribed energy, and the ion
beam is directed at the surface of the substrate. The energetic
ions in the beam penetrate into the bulk of the substrate material
and are embedded into the crystalline lattice of the substrate
material to form a region of desired conductivity.
[0006] Such an ion implanter may be used to implant desired dopants
into a silicon substrate to form solar cells. These solar cells
provide pollution-free, equal-access energy using a recurring
natural resource. Due to environmental concerns and rising energy
costs, solar cells are becoming more globally important. Any
reduced cost to the manufacture or increases in production of
high-performance solar cells or any efficiency improvement to
high-performance solar cells would have a positive impact on the
implementation of solar cells worldwide. This will enable the wider
availability of this clean energy technology.
[0007] Solar cells may require doping to improve efficiency. FIG. 1
is a cross-sectional view of a selective emitter solar cell. It may
increase efficiency to dope the emitter 200 and provide additional
dopant to the regions 201 under the contacts 202. More heavily
doping the regions 201 improves conductivity and having less doping
between the contacts 202 improves charge collection. The contacts
202 may only be spaced approximately 2-3 mm apart. The regions 201
may only be approximately 100-300 .mu.m across.
[0008] FIG. 2 is a cross-sectional view of an interdigitated back
contact (IBC) solar cell. In the IBC solar cell, the junction is on
the back of the solar cell. The doping pattern is alternating
p-type and n-type dopant regions in this particular embodiment. The
p+ emitter 203 and the n+ back surface field 204 may be doped. This
doping may enable the junction in the IBC solar cell to function or
have increased efficiency.
[0009] In the past, solar cells have been doped using a
dopant-containing glass or a paste that is heated to diffuse
dopants into the solar cell. This does not allow precise doping of
the various regions of the solar cell and, if voids, air bubbles,
or contaminants are present, non-uniform doping may occur. Solar
cells could benefit from ion implantation because ion implantation
allows precise doping of the solar cell. Ion implantation of solar
cells, however, may require a certain pattern of dopants or that
only certain regions of the solar cell substrate are implanted with
ions. Previously, implantation of only certain regions of a
substrate has been accomplished using photoresist and ion
implantation. Use of photoresist, however, would add an extra cost
to solar cell production because extra process steps are involved.
Other hard masks on the solar cell surface likewise are expensive
and require extra steps. Accordingly, there is a need in the art
for an improved method of implanting through a mask and, more
particularly, a health monitor for a mask used for ion
implantation.
SUMMARY OF THE INVENTION
[0010] Exemplary embodiments of the present invention are directed
to an apparatus and method of determining alignment of a mask in an
ion implanter. In an exemplary method, an ion beam is directed
through a plurality of apertures of a mask toward a platen
configured to support a target substrate. An ion current
measurement device is disposed behind the mask a substantially
co-planar relationship with respect to the target substrate as if
the substrate is positioned on said platen. The ion current
measurement device is translated across the ion beam. The position
of the ion current measurement device is recorded as it translates
across the ion beam. A current of the ion beam directed through the
plurality of apertures of the mask is measured using the ion
current measurement device at the recorded positions. A current
signal is generated in response to the measured ion beam current
from the ion current measurement device at each of the recorded
positions. The current signal is transmitted to a controller and a
control signal is generated by the controller and is used to
position at least one of the ion beam or the mask based on the
control signal such that a mean ion beam angle is centered with
respect to a center one of the plurality of apertures of the
mask.
[0011] In an exemplary embodiment, an ion implanter system includes
an ion source, a beam line assembly, a mask, an ion current
measurement device and a controller. The beam line assembly is
configured to extract ions from the ion source to form an ion beam
and direct the ion beam toward a a platen. The mask is disposed in
front of the platen. The mask has a plurality of apertures to allow
respective portions of the ion beam through the mask toward a said
platen. The ion current measurement device is disposed
substantially co-planarly with the surface of the target substrate
as if the target substrate was positioned on the platen. The ion
current measurement device is configured to translate across the
ion beam co-planarly with respect to the surface of the target
substrate. The ion current measurement device is also configured to
generate signals proportional to the ion current received through
the apertures as the measurement device translates across the ion
beam. The controller is configured to receive the signals from the
ion current measurement device and determine an orientation of the
mask with respect to the target substrate such that angles of the
ion beam through one or more of the'plurality of apertures in the
mask are aligned.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of a selective emitter
solar cell;
[0013] FIG. 2 is a cross-sectional view of an interdigitated back
contact solar cell;
[0014] FIG. 3A is a block diagram of a representative ion implanter
in accordance with an embodiment of the present disclosure;
[0015] FIG. 3B is a cross-sectional view of implantation through a
mask;
[0016] FIG. 4 is a front schematic view of implantation through a
mask using a Faraday probe in accordance with an embodiment of the
present disclosure;
[0017] FIG. 5A is a schematic perspective view of implantation
through a mask using a Faraday probe in accordance with an
embodiment of the present disclosure.
[0018] FIG. 5B is a top cross-sectional schematic view of
implantation through a mask using a Faraday probe in accordance
with an embodiment of the present disclosure;
[0019] FIG. 6 is a first top cross-sectional view of mask-ion beam
angular alignment in accordance with an embodiment of the present
disclosure;
[0020] FIG. 7 is a second top cross-sectional view of mask-ion beam
angular alignment in accordance with an embodiment of the present
disclosure;
[0021] FIG. 8 is a first top cross-sectional view of mask-substrate
alignment in accordance with an embodiment of the present
disclosure;
[0022] FIG. 9 is a second top cross-sectional view of
mask-substrate alignment in accordance with an embodiment of the
present disclosure;
[0023] FIG. 9A illustrates a feature profile associated with a
large gap between a mask and a substrate or platen.
[0024] FIG. 9B illustrates a signal profile for a mask having worn
apertures overlayed on a signal profile for a mask having non-worn
apertures.
[0025] FIG. 10 is a front perspective view of an embodiment of a
Faraday probe to test for mask erosion in accordance with an
embodiment of the present disclosure; and
[0026] FIGS. 11-13 are front perspective views of the embodiment of
a Faraday probe to test for mask erosion of
DETAILED DESCRIPTION
[0027] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention,
however, may be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. In the drawings, like
numbers refer to like elements throughout.
[0028] FIG. 3A is a block diagram of an ion implanter 115 including
an ion source chamber 120. A power supply 121 supplies the required
energy to source chamber 120 which is configured to generate ions
of a particular species. The generated ions are extracted from the
source through a series of electrodes 114 and formed into a beam
103 which passes through a mass analyzer magnet 116. The mass
analyzer is configured with a particular magnetic field such that
only the ions with a desired mass-to-charge ratio are able to
travel through the analyzer for maximum transmission through the
mass resolving slit 117. Ions of the desired species pass from mass
slit 117 through deceleration stage 118 to corrector magnet 119.
Corrector magnet 119 is energized to deflect ion beamlets in
accordance with the strength and direction of the applied magnetic
field to provide a ribbon beam targeted toward a work piece or
substrate positioned on support (e.g. platen) 102. In some
embodiments, a second deceleration stage 122 may be disposed
between corrector magnet 119 and support 102. The ions lose energy
when they collide with electrons and nuclei in the substrate and
come to rest at a desired depth within the substrate based on the
acceleration energy. A mask 104 and ion current measurement device
106 (shown in FIG. 4) are disposed proximate a process chamber
which houses platen 102.
[0029] FIG. 3B is an exploded cross-sectional view of implantation
of a substrate 100 utilizing a mask. When a specific pattern of ion
implantation in a substrate 100 is desired, a mask 104 may be
placed in front of substrate 100 in the path of an ion beam 103.
This mask 104 may be a shadow or proximity mask. The substrate 100
may be, for example, a solar cell which is placed on platen 102,
which may use electrostatic or physical force to retain the
substrate 100 theron. The mask 104 has apertures 105 that
correspond to the desired pattern of ion implantation in the
surface of substrate 100.
[0030] Use of the mask 104 eliminates process steps, such as
silkscreening or lithography, required for other ion implantation
techniques. However, it may be difficult to properly place the mask
104 relative to the substrate 100 to allow the desired pattern of
ion implantation. The mask 104, the ion beam 103, and the platen
102 all have linear and angular tolerance variations that may lead
to misalignment or misplacement of the mask 104.
[0031] FIG. 4 is a front schematic, view of implantation assembly
including a mask using a Faraday probe positioned parallel or
co-planarly with substrate 100 as if the substrate was positioned
on the platen 102 in the exemplary ion implanter shown in FIG. 3A.
The mask 104 includes a plurality of apertures 105 and is disposed
in front of the substrate 100 (partially outlined with dotted lines
behind the mask 104). The apertures 105 may also be configured as
holes, slots or other geometry configured to allow portions of the
ion beam through the mask. The mask 104 may be translated or
positioned in multiple axes using a translation mechanism 108. This
translation mechanism 108 may be a servo motor used to variably
position the mask linearly with respect to a distance from
substrate 100 and angularly with respect to the transmission of ion
beam in the z direction through the apertures. The substrate 100
may be scanned behind the mask 104 in one embodiment to obtain a
uniform pattern of implanted regions. The implanted regions may
resemble "stripes" across the surface of the substrate 100 in the X
and Y directions. For proper operation, the mask 104 must be
aligned (as described below) with substrate 100 as well as the ion
beam implanted through the apertures 105. Over time, the mask 104
may erode and the apertures 105 may become incorrectly sized or
have incorrect dimensions, thereby compromising a desired implant
profile.
[0032] The Faraday probe 106 is disposed behind mask 104 and is
configured to move in the X direction across the ion beam 103 when
the substrate 100 is not positioned on platen 102. The Faraday
probe is position on the same plane (i.e. the Z direction) as the
surface 100a of substrate 100 as of the substrate was positioned on
platen 102. The Faraday probe 106, or Faraday cup, is used to
measure the current of ion beam 103 incident on the same plane as
surface 100a to mimic implantation of regions of substrate 100
aligned with apertures 105 of mask 104 as if the substrate 100 was
positioned on the platen 102. Alternatively, multiple Faraday cups
may be included on Faraday probe 106 or multiple Faraday probes 106
may also be employed. The Faraday probe 106 is positioned behind
the mask 104 and coplanar with a surface 100a of substrate 100 in
place of substrate 100 to mimic implantation of the ion beam in the
substrate. Faraday probe 106 is configured to move in the X
direction via translation mechanism 107, which may be, for example,
one or more servo motors. Faraday probe 106 is connected to a
current measurement device 109. In this manner, the Faraday probe
106 receives the current of the incident ion beam 103 as if it were
substrate 100 and measurement device 109 measures the current that
travels from the Faraday probe 106 to ground. This current is
converted to a control signal which is supplied to controller
110.
[0033] The controller 110 reads the control signal from the current
measurement device 109 and determines if position correction is
necessary for the mask 104 or ion beam 103. The controller 110 can
send signals to the translation mechanism 108, the translation
mechanism 107, or another system or component to correct
positioning of the mask or to translate the Faraday probe. In one
embodiment, a separate motion control system may be used to process
the new desired positioning requirements and to drive the various
mechanisms, systems, and components. The controller 110 also may
adjust the ion beam or substrate 100. Use of the Faraday probe 106
enables more accurate placement of the mask 104, substrate 100, and
ion beam and improves implantation of the substrate 100 by
optimally aligning the apertures 105 of mask 104 with the substrate
100 when the substrate is positioned on platen 102.
[0034] FIG. 5A is a schematic perspective view of ion beam 103
portions of which travel through the apertures of mask 104. As can
be seen, the mask 104 is orthogonal to the direction of travel of
the ion beam 103 (i.e. Z direction). As the ion beam 103 travels
through the apertures of mask 104, portions of the ion beam
103.sub.1 . . . 103.sub.N would form "stripes" of dopant
implantation across the surface of the substrate when the substrate
is positioned on the platen. The other portions of the ion beam 103
incident are blocked by the area of the mask between the apertures.
Faraday probe 106 is positioned behind mask 104 and translates in
the X direction across the ion beam portions 103.sub.1 . . .
103.sub.N. Faraday probe 106 is illustrated as being positioned
toward the top (in the Y direction) of ion beam 103. However, this
is for explanatory purposes and the probe 106 may be positioned
anywhere along the Y axis of the ion beam 103. However, it is
optimal that the Faraday probe 106 be parallel or substantially
co-planar with the surface 100a (shown in FIG. 4) in the z
direction so that the probe receives substantially the same ion
beam portions 103.sub.1 . . . 103.sub.N that would be received by
the substrate 100 as if the substrate was receiving implantation of
the ion beam 103 as the probe translates across the beam 103 in the
X direction. In this manner, the ion current of the portions of the
beam that travel through the apertures is measured by the Faraday
probe. In addition, the position of the probe 106 is monitored such
that variations in ion beam current detected by the probe may be
correlated with a particular one or more of the plurality apertures
in mask 104. For example, over time the edges of the apertures of
the mask 104 may erode from constant exposure to beam 103. This may
cause the width of one or more apertures to enlarge beyond a given
implant and alignment tolerance level. By monitoring the position
of the probe as it translates across the ion beam portions
103.sub.1 . . . 103.sub.N, the ion beam current measured at a
particular one of the apertures may be determined to be outside a
given tolerance level. Accordingly, the condition of the mask 104
and more particularly the condition of the apertures of the mask
may be monitored. It has been found that an increase in the width
of an aperture 105 of up to about 20% can be tolerated without
compromising the integrity of an implant profile for a solar cell.
This is due to the fact that a masked area (i.e. the area of the
substrate not disposed behind one of the apertures 105) is
typically more heavily doped than the portions of the substrate
behind the apertures 105 of an emitter cell which are more lightly
doped. As the edges of an aperture 105 erode, the emitter area
becomes more heavily doped than designed. This may compromise solar
cell performance.
[0035] FIG. 5B is a top cross-sectional view of the ion beam shown
in FIG. 5A through mask 104 and the positioning of the Faraday
probe 106 with respect to the mask and a substrate 100 as if the
substrate was present. As mentioned above, the Faraday probe 106
translates in the X direction behind mask 104 as indicated by the
arrow 111. As the Faraday probe 106 translates behind the mask 104,
a signal is generated proportional to the exposed current of the
ion beam 103. This current and the known position of the Faraday
probe 106 monitor the health or condition of mask 104. The Faraday
probe 106 can, for example, be used to properly position the mask
104, optimize the spacing in the Z direction between the mask 104
and the substrate 100, monitor the mask 104 for excessive wear or
erosion, monitor the mask 104 for fracturing, or monitor the mask
104 for thermal control.
[0036] The signal generated by the probe 106, which is proportional
to the ion beam current incident on the probe as it translates
across the beam in the X direction indicated by arrow 111, also
provides alignment information with respect to the ion beam 103 and
mask 104. In particular, if the mask 104 is aligned with the beam
such that the angles of the ion beam 103 emanating from the
apertures 105 of the mask 104 cause the beam portions 103.sub.1 . .
. 103.sub.N (shown in FIG. 5A) to fall within the desired implant
region; then the probe 106 may detect a desired ion beam current
range indicating that the mask 104 is aligned with the divergent
angles of beam 103. Because the beam 103 is composed of
like-charged molecules, the beam 103 will naturally diverge causing
divergent beam angles. If however, the probe 106 measures ion beam
current emanating from a particular one or more of the apertures
105 that is not within the desired range, this indicates that the
mask 104 and beam 103 are not aligned or at least not optimally
aligned to satisfy implant region requirements for an intended
substrate 100.
[0037] FIG. 6 is a first top cross-sectional view of mask-ion beam
angular alignment. The Faraday probe 106 may be used for alignment
between the mask 104 and the ion beam 103. The mask 104 can be
oriented with respect to the ion beam 103 so that the beam angles
generated by the apertures 105 will implant the proper regions of
an intended substrate 100. Additionally, by aligning the mask 104
with respect to the existing beam divergence angles of the ion beam
103, the mask 104 can optimize the available current of the ion
beam 103. The angle of the ion beam 103 that passes through the
apertures 105 is fixed, and, thus, the amplitude of the ion beam
103 measured by the Faraday probe 106 is optimal when the angle of
the ion beam 103 and angle of the mask 104 are aligned. In other
words, since the admittance angles through the apertures 105 of
mask 104 are fixed (i.e. the apertures are positioned through
particular locations across the mask) the ion beam current measured
by the probe 106 as it translates across the beam in the X
direction is optimal when the beam divergence angles and mask
angles are aligned. Thus, by using the probe 106 to provide
feedback of the amount of ion beam current detected through the
apertures 104, alignment of the mask 100 with respect to the
divergent angles of beam 103 as it travels through the mask can
optimize the available ion beam current incident on an intended
substrate 100. Consequently, by maximizing the amount of beam
current incident on the intended substrate 100, throughput of the
implanter may be optimized. The angles of the ion beam 103 in FIGS.
6-7 are exaggerated for clarity.
[0038] In FIG. 6, the mask 104 is shown misaligned to the ion beam
103. In this particular instance, the peak beam angles are not
centered on the midpoint of the mask 104. Instead, the mean beam
angle 600 of the ion beam 103 is off-center with respect to the
mask 104. To correct this, the mask 104 may be translated by a
certain angle or distance to center the mean beam angle 600 to
coincide with the center of the mask 104. In another instance, the
beam 103 is adjusted to center the mean beam angle 600 to coincide
with the center of the mask 104. FIG. 7 is a second top
cross-sectional view of mask-ion beam angular alignment. In this
embodiment, the mean beam angle 600 is coincides with the center of
the mask 104.
[0039] FIG. 8 is a first top cross-sectional view of mask-substrate
alignment. FIG. 8 illustrates an ideal case where the ion beam 103
is aligned with the mask 104 and the beam passes through the
apertures 105 optimally. The resulting implant region matches the
size (width in the x direction and length in the y direction) of
the apertures 105. However, since the ion beam 103 is composed of
like-charged molecules or atoms as noted above, the beam will
diverge some small amount.
[0040] FIG. 9 is a second top cross-sectional view of
mask-substrate alignment. FIG. 9 illustrates beam divergence. The
ion beam 103 that passes through the apertures 105 does not have
the same dimensions at the platen 102 as it did leaving the
apertures 105. This divergence will vary based on the conditions of
the ion beam 103. A small gap between the mask 104 and platen 102
or substrate 100 on the platen 102 may minimize the effects of beam
divergence. Minimizing this gap between the mask 104 and platen 102
or substrate 100 on the platen 102 may ensure that the actual
implant region will be similar to the desired implant region by
minimizing the distance between the mask and the substrate within
which the ion beam 103 has available to diverge. However, the gap
between the mask 104 and platen 102 or substrate 100 on the platen
102 may vary as a result of machining tolerances, assembly
tolerances, systems loads, or other reasons. Given the
characteristic of the ion beam to diverge as it travels, it is
important to maintain as small a gap as possible in the Z direction
between the mask 104 and the substrate 100. If the gap is too
large, then the implanted region will exceed the intended target
region on the substrate. In addition, the mask 104 may include
alternatively configured holes, slots, etc. (as mentioned above)
that form a two dimensional pattern on the substrate 100. In this
embodiment, the angles in the X and Y direction determine the
implant pattern fidelity.
[0041] To optimize the gap between the mask 104 and platen 102 or
substrate 100 on the platen 102, the Faraday probe 106 creates a
feature profile measurement behind the mask 104. For example, FIG.
9A illustrates a feature profile where a large gap exists between
the mask 104 and platen 102 or substrate 100. As can be seen, a
larger gap between the mask 104 and platen 102 or substrate 100 on
the platen 102 will cause the resulting profile to the Faraday
probe 106 to be wider in dimension and shorter in peak amplitude.
In one embodiment, the gap between the mask 104 and platen 102 or
substrate 100 on the platen 102 can be adjusted by servo motors,
and then the Faraday probe 106 can confirm the profiles are within
the specification for the substrate 100.
[0042] Over time, an ion beam 103 will erode the material of the
mask 104 and in particular the edges of the apertures 105. This
erosion is caused at least in part by surface sputtering and
thermal cycling. Eventually the mask 104 will need to be replaced
because the apertures 105 have eroded past a specific tolerance or
have incorrect dimensions. A Faraday probe 106 can scan behind the
mask 104 to monitor for this erosion. In one instance, an eroded
mask 104 will exhibit a signal profile that has a high amplitude
and large line width. FIG. 9B illustrates a signal profile for a
mask having worn apertures 105 (shaded region 105a) overlayed on a
signal profile for a mask having non-worn apertures (illustrated by
middle portions 105b). In particular, the current signal profile of
the shaded regions shows a signal having a higher amplitude and
larger line width than the signal associated with a mask having
non-worn apertures. Since the height of the ion beam 103 can vary,
the erosion of the mask 104 may not be uniform from one side of the
aperture 105 to the opposite side of the aperture 105. In one
particular embodiment, the Faraday probe 106 is positioned at an
angle with respect to the mask 104.
[0043] FIG. 10 is a front perspective view of an embodiment of a
Faraday probe to test for mask erosion. Because the Faraday probe
106 is at an angle with respect to the mask 104, the Faraday probe
106 is only exposed to a portion of the aperture 105 as it scans.
FIGS. 11-13 are front perspective views of the embodiment of a
Faraday probe to test for mask erosion of FIG. 10 during
translation of the Faraday probe. A profile for the mask 104 will
indicate if the dimensions of the apertures 105 are not
uniform.
[0044] In addition to erosion, the ion beam 103 may induce
deposition or coating of the mask 104. In this case, rather than
the apertures 105 growing in dimension, the apertures 105 will
shrink or narrow in dimension. As with erosion, this shrinking or
narrowing of the apertures 105 may vary from one side of the
aperture 105 to the other side of the aperture 105 as well as along
the length of the aperture. A Faraday probe 106 can scan behind the
mask 104 to monitor for coating. In one instance, a coated mask 104
with narrowed or shrunken apertures 105 will exhibit a signal
profile that has a low amplitude and small line width as compared
to that shown in FIG. 9B.
[0045] The mask 104 may be composed of mechanically delicate
materials or features. Thus, fracturing of the mask 104 is a
concern. This fracturing may be caused by, for example, thermal
loads, vibration, or erosion. If the mask 104 fractures, the
Faraday probe 106 will detect the missing portion of the probe. The
broken or missing portion of the mask 104 will be evident from the
signal displaying ion beam 103 current in an unexpected area.
Should this happen, in one embodiment, the Faraday probe 106
indicates to the system that a fatal error has occurred and that
repair is required. Furthermore, by detecting such a fractured mask
improper implantation is prevented.
[0046] The mask 104 is exposed to strikes by the ion beam 103
during its lifetime. The amount of power dropped into the mask 104
depends on the parameters of the ion beam 103, such as total
voltage or beam current. This power dropped into the mask 104 will
create a thermal load on the mask 104. The resulting thermal
expansion of the material that the mask 104 is composed of may
cause positioning errors of the mask 104 or the apertures 105.
Since this material in the mask 104 expands at a rate proportional
to the thermal excursion of the mask 104, the Faraday probe 106 can
estimate the temperature of the mask 104 to ensure the mask 104
stays within any functional limits. The pitch of the signal will
vary with the temperature of the mask 104. Thus, as the apertures
105 changes size or dimensions due to thermal load, the Faraday
probe 106 can measure these changes.
[0047] While the embodiments above use a Faraday probe 106, other
measurement systems, such as an optical digital imaging system, may
be used alone or in conjunction with the Faraday probe 106. In this
particular embodiment, the substrate 100 is examined after
implantation. The resulting image is captured and processed. The
implanted regions on the substrate 100 will demonstrate the same
signal variation as described above for each of the conditions or
tests performed by the Faraday probe 106. In another embodiment the
mask 104 may be examined by optical imaging and the resulting image
captured and processed. The features on the mask 104 should
demonstrate the same signal variation as described above for each
of the conditions or tests performed by the Faraday probe 106.
Periodic inspection of the mask 104 should match the results of the
Faraday probe 106.
[0048] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Furthermore, although the present disclosure has been
described herein in the context of a particular implementation in a
particular environment for a particular purpose, those of ordinary
skill in the art will recognize that its usefulness is not limited
thereto and that the present disclosure may be beneficially
implemented in any number of environments for any number of
purposes. Accordingly, the claims set forth below should be
construed in view of the full breadth and spirit of the present
disclosure as described herein.
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